EM73A89B Datasheet, PDF (12/58 Pages) ELAN Microelectronics Corp – 4-BIT MICRO-CONTROLLER FOR LCD PRODUCT

(5) Other operations:
EM73A89B
4-BIT MICRO-CONTROLLER FOR LCD PRODUCT
Preliminary
For 1-byte instruction execution: PC + 1
For 2-byte instruction execution: PC + 2
For 3-byte instruction execution: PC + 3
ACCUMULATOR
Accumulator(ACC) is a 4-bit data register for temporary data storage. For the arithematic, logic and
comparative opertion.., ACC plays a role which holds the source data and result.
FLAGS
There are three kinds of flag, CF ( Carry flag ), ZF ( Zero flag ) and SF ( Status flag ), these three 1-bit flags
are included by the arithematic, logic and comparative .... operation.
All flags will be put into stack when an interrupt subroutine is served, and the flags will be restored after
RTI instruction is executed.
(1) Carry Flag ( CF )
The carry flag is affected by the following operations:
a. Addition : CF as a carry out indicator, under addition operation, when a carry-out occures, the CF is "1",
likewise, if the operation has no carry-out, CF is "0".
b. Subtraction : CF as a borrow-in indicator, under subtraction operation, when a borrow occures, the CF
is "0", likewise, if there is no borrow-in, the CF is "1".
c. Comparision : CF as a borrow-in indicator for Comparision operation as in the subtraction operation.
d. Rotation : CF shifts into the empty bit of accumulator for the rotation and holds the shift out data after
rotation.
e. CF test instruction : Under TFCFC instruction, the CF content is sent into SF then clear itself as "0".
Under TTSFC instruction, the CF content is sent into SF then set itself as "1".
(2) Zero Flag ( ZF )
ZF is affected by the result of ALU, if the ALU operation generates a "0" result, the ZF is "1", likewise, the
ZF is "0".
(3) Status Flag ( SF )
The SF is affected by instruction operation and system status.
a. SF is initiated to "1" for reset condition.
b. Branch instruction is decided by SF, when SF=1, branch condition is satisified, likewise, when SF = 0,
branch condition is unsatisified.
* This specification are subject to be changed without notice.
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